1. Field of the Invention
The present invention relates to a light emitting display and a method of driving the same.
2. Description of the Related Art
A light emitting device is a spontaneous light emitting device that comprises an light emitting unit formed between two electrodes.
A light emitting display that comprises the light emitting device has a higher response speed and a lower direct current (DC) driving voltage than a passive light emitting device that requires an additional light source such as a liquid crystal display (LCD), and the light emitting display can be made ultra slim. Therefore, the light emitting display can be wall-mounted or portable.
The light emitting device embodies colors using pixels in which red, blue, and green sub pixels represent one color.
The light emitting device is divided into a passive matrix organic light emitting device (PMOLED) and an active matrix organic light emitting device (AMOLED) in which thin film transistors (TFT) are used in accordance with a method of driving the sub pixels.
FIG. 1 is a cross-sectional view of a conventional AMOLED.
Referring to FIG. 1, the conventional AMOLED 30 comprises a thin film transistor (TFT) 34 formed on a substrate 32, a pixel electrode 36 connected to the drain of the TFT 34, multiple organic light emitting layers 38 laminated on the pixel electrode 36, a cathode electrode 40 formed on the organic light emitting layers 38, and a protective layer 42 formed on the cathode electrode 40.
In the conventional AMOLED 30, a data signal is applied to the source of the TFT 34 when a scan signal is applied to the gate of the TFT 34 to supply holes and electrons to the organic light emitting layers 38 through the pixel electrode 36 and the cathode electrode 40 so that the holes and the electrons are re-combined with each other to emit light.
When the conventional AMOLED 30 is initially driven, the brightness of the conventional AMOLED 30 unstably increases and is stabilized after a certain amount of time.
FIG. 2 is a graph illustrating the brightness characteristic of the conventional AMOLED.
Referring to FIG. 2, when the conventional AMOLED 30 is initially driven, the brightness of the conventional AMOLED 30 rapidly increases and then is reduced as illustrated in the graph A, and uniform brightness is obtained after a certain amount of time.
When the conventional AMOLED 30 having the above-described brightness characteristic is continuously driven, the TFT 34 and the organic light emitting layers 38 are damaged so that the life span of the conventional AMOLED 30 is rapidly reduced.
Therefore, in the case of the light emitting display that displays an image using the conventional AMOLED 30, it is difficult to commercialize the light emitting display due to the short life time of the conventional AMOLED 30.